The vertebrate neural crest is a remarkable system that gives rise to a wide range of cell types during embryogenesis. Some of the neural crest-derived lineages include the neuronal and support cells of the peripheral nervous system, structural components of the face and skull, outflow tract of the heart and pigment-producing melanocytes. This diverse and complex system offers a wonderful opportunity to study many of the fundamental biological problems including lineage determination, cell-cell interaction, directed migration and differentiation. Aberrant development of these cells in humans result in many congenital diseases involving the neurological defects, craniofacial and heart malformations, and pigmentation diseases. We have been studying the role of the endothelin receptor-B (Ednrb) gene, encoding a seven-transmembrane G-coupled receptor, that is essential for the development of the neural crest-derived melanocytes and enteric neurons in mice. Mutations of the Ednrb gene have been identified in the patients with Hirschsprung and Waardenburg syndrome. Using the tetracycline-inducible system in mice, we have determined that Ednrb is required at a very specific timepoint for the migration of these cells during embryogenesis. In addition, the insertion of the lacZ marker gene into the Ednrb locus allowed us to visualize the fate of these cells in the mutant animals. We would like to further define the in vivo mechanisms mediated by EDNRB by utilizing the various genetic manipulation techniques that are available for studies in the mouse with the following specific aims: 1) To investigate if the specific migratory pathway taken by the neural crest derived-melanoblasts is dictated by its cell fate? 2) To identify factors affecting determination of melanoblasts and enteric neuroblasts from the pluripotent neural crest cells? 3) To perturb the concentration of the EDNRB ligand encountered by the migrating crest cells and to determine the EDNRB-mediated cellular mechanisms in the developing mouse embryos.